diff --git a/.github/workflows/skill-frontmatter.yml b/.github/workflows/skill-frontmatter.yml
index 3a7e9f0..b84a56d 100644
--- a/.github/workflows/skill-frontmatter.yml
+++ b/.github/workflows/skill-frontmatter.yml
@@ -18,7 +18,7 @@ jobs:
     name: Reject multi-line YAML descriptions
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
 
       - name: Check SKILL.md descriptions are single-line
         run: |
diff --git a/.github/workflows/validate-plugins.yml b/.github/workflows/validate-plugins.yml
index 686c072..4fa4101 100644
--- a/.github/workflows/validate-plugins.yml
+++ b/.github/workflows/validate-plugins.yml
@@ -17,6 +17,6 @@ jobs:
   validate-plugins:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - name: Validate plugin registrations
         run: node scripts/validate-plugins.mjs